Replicated optical elements include refractive elements such as lenses and diffractive and/or refractive micro-optical elements for influencing an optical beam in a pre-defined manner.
When optical elements are produced by replication, there is often a basic configuration involving a substrate and replication material on a surface thereof. The replication material can be shaped and hardened in the course of a replication process. Often, the dimension perpendicular to the named substrate surface—the thickness or height of the replicated structures, also termed z-dimension—is important and is well-defined and controlled. Since the other dimensions of the element are defined by the replication tool—this being the nature of the replication process—also the volume of the replicated element is well defined. However, small volumes of dispensed liquid or viscous material are generally difficult and costly to control. Since elements that are only partially filled are defective and lost, it is therefore advantageous to dispense excess replication material. By this, one makes sure that also for replication material volumes that fluctuate between different elements, no or only few elements are lost.
Of special interest are the wafer-scale fabrication processes, where an array of optical elements is fabricated on a disk-like (“wafer-”) structure, which subsequent to replication is separated (“diced”) into the individual elements or stacked on other wafer-like elements and after stacking separated into the individual elements. Wafer scale refers to the size of disk like or plate like substrates of sizes comparable to semiconductor wafers, such as disks having diameters between 2 in and 12 in. In conventional wafer-scale replication processes, replication material for the entire, wafer-scale replica is disposed on the substrate in a single blob. However, there might be areas sideward of the element where replication material is not wanted in later replication steps. In certain applications, the fabricated elements must for example be used in combination with other elements, and the residual material will impair the function of the combined structure.
In such an array replication process, excess material can ooze out sideward from the element volume. For example, miniature optical lenses can be replicated above the surface of a wafer carrying semiconductor chips each embodying a CCD or CMOS-camera sensor array. The residual material, if it covers critical areas, can interfere with further processing steps of the stack comprising the semiconductor wafer and the lenses, e.g., bonding.
A structured (or micro-structured) element can be manufactured by replicating/shaping (moulding or embossing or the like) a 3D-structure in a preliminary product using a replication tool. The replication tool comprises a spacer portion protruding from a replication surface. A replicated micro-optical element is referred to as replica.
The spacer portions can allow for an automated and accurate thickness control of the deformable material on the substrate. They can include “leg like” structures built into the tool. In addition, the spacers can prevent the deformation of the micro optical topography since the spacers protrude further than the highest structural features on a tool.
The spacer portion is preferably available in a manner that it is distributed over at least a portion of the replication tool, for example, over the entire replication tool or at the edge. This means that features of the spacer portion are present in an essential fraction of the replication tool, for example, the spacer portion includes a plurality of spacers distributed over the replication surface of the replication tool. The spacers can allow for an automated and accurate thickness control of the replication material layer.
The replication process can be an embossing process, where the plastically deformable or viscous or liquid replication material for the product to be shaped is placed on a surface of a substrate, which can have any size. In the embossing step, the spacer portions abut against the top surface of the substrate. The surface thus serves as a stop face for the embossing, which can control the thickness (height, z-dimension) of the replicated elements. Other ways of controlling the z-dimension include measuring the distance between a tool plane and a substrate plane, and actively adjusting this distance at different places by a robot. The embossing step and/or the spacer portion, however, can cause residual material to remain in the areas between the elements, and for example, also around the periphery of each of the elements.